Abstract
Abstract Outcropping granites in the Precambrian crystalline schists of the Betsileo region, central southwestern Madagascar, frequently occur in interstratified shells. These granites are foliated and grade into coarsely banded migmatitic rocks; their structure is granoblastic. The granitic facies are alkaline, whereas the migmatites are calcalkaline. Chemical comparison with the surrounding gneisses shows that the granitization is the result of alkaline metasomatism of the gneiss. The exchanges affect only 6 to 12 percent of the cations of the standard cell. These granites probably date from the Eocambrian orogeny.
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